a knife that you have to flip around to open.....cool...even more ways to slice your fingers. i guess it would be ok for something different if you have a knife collection or something, but not too pratical. a good quality folding 3 inch or so pocket knife would serve you much better, and you could get a leather holder for your belt to keep it in.
Anyways.. thebigdintx is right.. A butterfly knife is cool only to impress your friends. But if your looking for pratical use, get one of the pocket knives. About a 4-5 inch one. Oil it up a bit, so you can just flick it with your wrist, and pop it out. I have one of those!! Woohoo! Their freakin nice.